Eutectic beams are commonly used to refrigerate the cargo space of a small delivery, truck. A eutectic beam works on the principal of heat transfer during freezing and melting of an eutectic solution, such as sodium nitrate (NaNO.sub.3), ammonium chloride (NH.sub.4 Cl), brine, and the like. The specific eutectic solution used is determined by the desired temperature of the cargo space. An eutectic beam may be charged during night storage of an associated truck, for example, by connecting the eutectic beam to an external condensing unit via flexible hoses; or, by operating a refrigeration system on the truck from a commercial power supply. If the truck has a refrigeration system, an eutectic beam may also be charged while the truck is in use.
An eutectic beam comprises a housing, an eutectic solution in the housing, and a metallic cooling pipe in the eutectic solution. When the eutectic solution is to be frozen, a refrigeration system, i.e., a condensing unit, is connected to the metallic cooling pipe, and a refrigerant is passed through the metallic pipe. The metallic pipe functions as an evaporator, removing heat from the eutectic solution until it is frozen. For purposes of simplicity, the metallic pipe in an eutectic beam will be hereinafter called the evaporator tube.
Eutectic beams of which I am aware commonly utilize plastic for the housing, such as polyethylene, with the metallic evaporator tube being constructed either of copper, or steel tubing coated with a 1 mm thick protective layer of polyethylene.
Plastic is commonly used for the housing, instead of metal, because of corrosion problems, notwithstanding that the plastic reduces, the efficiency of an eutectic beam due to its lower thermal conductivity.
Copper is used for some evaporator tubes, even though it corrodes rather rapidly in commonly used eutectic solutions, with and without corrosion inhibitors, requiring costly replacement at regular maintenance intervals. The use of plastic coated steel tubing for the evaporator tube solves the corrosion problem, and is thus used in some eutectic beams for that reason. Plastic coated pipe, however, is much heavier than copper, and it has the further disadvantage of having a much poorer thermal conductivity than copper.
It would thus be desirable, and it is an object of the invention, to improve both the life and efficiency of an eutectic beam, without concomitant offsetting disadvantages, such as cost.